This invention relates to a numbering device for use in an offset printing machine.
According to the conventional numbering device for use in the offset printing machine, the numbering device is accommodated in an impression cylinder of the printing machine to simultaneously achieve ordinary printing and numbering on the impression cylinder. In this type, however, since the impression cylinder is commonly used for both ordinary printing and numbering, a special mechanism is required to be installed in the impression cylinder. For example, since the distance between the central axis of a blanket cylinder and the central axis of a shaft for attaching the numbering device cannot be uniform relative to the central axis of the impression cylinder due to machining of mechanical parts, a paper or thin sheet is required to be wrapped around the impression cylinder in order to compensate the error.
In this case, reference numeral surface of a numbering device may bite into the sheet to create recessed portion, resulting in degrading the printing efficiency. In order to obviate this drawback, the sheet should be replaced with new one, which in turn, lowers workability and operabilities.
Another type of the conventional numbering device has been provided, wherein the numbering device is accommodated in a delivery section, so that the ordinary printing is achieved at the impression cylinder, and thereafter, number printing is achieved at the delivery section.
According to this type of device, since the numbering operation is achieved immediately before the fall of the printed sheet to provide printed stack, sheet to be subject to numbering is in an unstable condition. That is, the numbering operation is carried out at a chain-delivering portion, in which leading edge of the paper before numbering operation is merely supported by a delivery gripper, while the tail end of the paper is urged toward the direction of the falling, so that the paper may be corrugated or laterally displaced when the paper is about to be in numbering operation. Therefore, it would be almost impossible to accurately achieve numbering at the predetermined position of the sheet.
Further, the printed sheets such as slips and ledges are required to be subject to numbering as well as perforating or slitting operations. According to the conventional printing machine, after the number printing operation, the sheets are perforated by the independent perforating means or slitter, and therefore, the sheets must be reset at the perforating means, resulting in causing the entire operations to be troublesome.